EP3748228A2 - Burner with reduced flame temperature and nitrogen oxide emission - Google Patents

Abstract

The invention relates to a burner 1 with a housing 2 on which a combustion tube 3 is arranged, wherein the combustion tube 3 has an opening 4 at the end facing away from the housing 2, and wherein the housing 2 has at least two separate channels 6, 7, 7 ', through which different substances, in particular a fuel and an oxidizer, flow through, which mix in a combustion chamber 8, the substances opening into a fuel nozzle system 5, 5' which is arranged essentially circularly and is set up so that it produces a leaner mixture on at least one outer ring 12 and a richer mixture on at least one inner ring 13, in particular a fuel / oxidizer mixture, the elements of the fuel nozzle system 5, 5 'being as thin, slender and streamlined as possible, the area ratio of the inner ring 13 to that of the outer ring 12 is 1: 2.5 to 1: 3.9, preferably 1: 3.1, and / or the maximum swirl angle (α) of the fuel nozzle y stems 5, 5 'on the outside between 30 ° to 60 °, preferably 48 °, and decreases continuously from the outside to the inside. The swirl elements can also be designed to be curved.

Description

The invention relates to a burner with reduced flame temperature and nitrogen oxide emissions.

For the combustion of the fuel mixed with an oxygen carrier, a burner with a burner head, which essentially has a tubular channel, in which the oxygen carrier, for example air, flows out via a fan and mixes with the fuel, for example gas, is used a distribution system is directed into a tubular channel. An ignition device ignites the mixture of oxygen carrier and fuel, which initiates combustion.

Such burner heads represent a burden for the environment, since they emit nitrogen oxides (NO _x ) generated during combustion into the atmosphere. For this reason, burners with burner heads have already been developed in which the production of these nitrogen oxides can be reduced.

From the Italian patent application 85 622 - A / 90 a burner head is known in which the reduction in nitrogen oxides is achieved with the aid of distributor devices when the fuel is supplied. The distributor is located inside the front part of the supply pipe for the combustion air and consists of annular spaces which run at right angles to the axis of the supply pipe and are delimited by coaxial rings which are connected to one another via spacer elements.

From the other Italian patent application VI 91 A 42 a burner consisting of a block is known, in which the nitrogen oxides are broken down in that part of the flue gases generated during the combustion is returned to the interior of the burner head.

In the further Italian patent application XI 91 A 166 A burner is proposed in which a series of openings are incorporated into the outer circumference of the supply duct for the combustion air in order to reduce the generation of nitrogen oxide.

From the DE 195 42 73 B4 a burner head for burners with a tubular body for supplying an oxygen carrier into a combustion chamber is known, in which one or more pipes are provided for supplying a fuel into the combustion chamber, the pipes running in the tubular body and via a feed channel with the Fuel are supplied. In addition, a converging transition piece is provided at the end of the tubular body, which protrudes into the combustion chamber, the convergence pointing into the interior of the combustion chamber. Furthermore, at least one ignition device is provided, which is located in the tubular f-body in the vicinity of the converging transition piece, the outlet opening of each pipe for the supply of fuel being within a zone of the tubular body which is delimited by the converging of the transition pieces and lies in the inclined wall surface of the transition piece, as a result of which the fuel flow passes essentially to the outside and into the zone of greater flow velocity of the oxygen carrier flow. In this way, the gas flow is directed against the outer area of the air flow, which is accelerated when passing through the converging transition piece and via it carries the gas flow far into the interior of the combustion chamber. At the same time, the acceleration of the air flow creates a negative pressure in the area of the combustion chamber, so that some of the flue gases generated during combustion are fed back into the flame. This results in a reduction in the flame temperature and a lower nitrogen oxide concentration.

In principle, generic burning devices are known which convert chemical energy into thermal energy in one burning process. At least one oxidizing agent, preferably air, is used in this firing process or oxygen, burned with a fuel in the combustion chamber in a continuous reaction with the release of heat. The heated exhaust gases are released into the open environment through the opening and can be used, for example, in all types of heating systems, drying systems, thermal post-combustion systems, environmental systems, curing ovens or in other process engineering systems. Commercially available, purified gases such as town, long-distance, natural or liquid gas and mixtures thereof come into consideration as fuel. Heating oil, petroleum and other liquid or pasty fuels can also be burned.

The burners generally known from the prior art can be divided into two categories. The first category includes burners in which the oxidizing agent is injected into the combustion chamber as a mixture with the fuel. Such burners are also referred to as premix burners. In contrast, burners of the second category have a separate feed line for the oxidizing agent and the fuel up to the combustion chamber, so that the two substances only mix in this. The burners of the first category have the advantage that the mixture of oxidizing agents and fuel is available in a very homogeneous mixture in the combustion chamber, but the disadvantage is that there is no absolute security against flashbacks. Such flashbacks are excluded in burners of the second category due to the separate feed of the oxidizing agent and the fuel. However, the homogeneity of the mixture in the combustion chamber is not optimal. In any case, it is worse than the mixture achieved by burners of the first category.

The aim of the invention is therefore to reconcile the advantages of burners of the second category with the advantages of burners of the first category, that is, on the one hand, to reliably exclude flashbacks, but at the same time to ensure high homogeneity of the mixture and thus both the flame temperature and the Reduce nitrogen emissions.

To achieve the best possible combination between safety and combustion, the DE 10 2018 112 540 Applicant already has a fuel nozzle system that is essentially circular and is set up so that it generates a leaner mixture on at least one outer ring and a richer mixture, in particular a fuel / oxidizer mixture, on at least one inner ring. Also the DE 10 2017 116 529 the applicant pursues the goal of optimizing the combustion process by achieving better homogeneity of the mixture in the combustion chamber.

The present invention develops the basic idea and improves these findings and studies.

According to the invention, it is now proposed that the elements of the fuel nozzle system be made as thin, slender and streamlined as possible. It has been found that turbulence occurs at each leading edge, since this air flow has to flow around every component built into the air flow. Recirculations also occur in the turbulence zones at the trailing edge located downstream. These eddies, in particular the recirculations, lead to a mixing of the inner richer and outer leaner fuel-air mixture. This in turn leads to an increased flame temperature and thus to increased nitrogen oxide formation.

It is therefore the aim of the present invention to avoid this turbulence as far as possible. This is achieved through the slim, thin design of all components used, which should also be made as streamlined as possible.

Alternatively or cumulatively, the invention also provides that the area ratio of the inner ring to the area ratio of the outer ring is 1: 2.5 to 1: 3.9, preferably exactly 1: 3.1.

Such an area ratio has proven to be optimal in various tests. It is partly dependent on the calorific value of the gas used. With area ratios of 1: <2.5, nitrogen oxide formation increases significantly with a stable flame. At area ratios of 1:> 3.9, the flame stability decreases without the nitrogen oxides further reducing.

Furthermore, it is alternatively or cumulatively provided that the maximum swirl angle (α) of the fuel nozzle system on the outside is between 30 ° to 60 °, preferably exactly 48 °.

At this angle of twist, the first small recirculations begin to form in the outer area. The twist must therefore not be greater than specified. On the other hand, the swirl is still strong enough to stabilize the flame. At lower helix angles, however, the flame becomes unstable.

In a further embodiment, the angle of twist (α) decreases continuously from the outside to the inside.

Since the inner, richer area burns more stably than the outer, leaner area, the swirl is only necessary to create stable conditions in the flame. However, there must be no jump in the twist between the inner, richer area and the outer, leaner area, as otherwise the inner and outer areas would mix at this shear surface. Since little or no twist is advantageous in the inner area, but twist is necessary in the outer area and no jump from the inside to the outside should be generated, the twist must decrease continuously from the outside to the inside.

Furthermore, it is alternatively or cumulatively provided that the swirl elements are designed in an arc shape. When generating the swirl, such arcuate blades form significantly fewer recirculations than straight blades. The air is carried along in the direction of flow, the direction change takes place gently along the arch.
In a further embodiment, it is provided that the helix angle (α) is on the inside at 0, that is to say decreases from the outside inwards to 0.

In one embodiment, the fuel nozzle system has a perforated plate upstream for homogenizing the air flow in front of the mixing unit over the entire cross section.

The combustion air supplied through the housing must hit the mixing unit with a flow velocity that is the same over the cross section, so that a homogeneous gas-air mixture inside and outside can arise. However, the deflection of the combustion air when it enters the burner housing results in very different flow speeds. These are canceled and homogenized by the proposed perforated plate in front of the mixing unit.

In order to avoid turbulence, the installation space between the perforated plate and the inner ring should only have electrodes and no other components. Any turbulence must be avoided before the air flow hits the mixing unit. In one embodiment, feeding the electrodes from the side is also conceivable. This would be an additional advantage for the burner, albeit rather difficult to achieve in practice.

Furthermore, at least one double-walled tube is provided for transporting fuel outside the housing cross-section to the fuel nozzle system. This arrangement also pursues the goal of not generating any turbulence.

In an alternative embodiment, at least one double-walled tube is provided on the very outside within the burner cross-section for transporting fuel on the edge of the housing cross-section to the fuel nozzle system. In this case, in which turbulence through the double-walled pipe cannot be avoided, they do less damage outside than inside.

The cross section of the swirl generator should be designed so that the fuel is guided inwards. In this way no additional gas ducts are necessary. Otherwise, these also generate turbulence and recirculation.

A partition wall can be provided between the interior and exterior of the fuel nozzle system. In this way, when the swirl is generated, the air flow is directed axially, possibly in addition to the perforated plate according to the invention in front of the mixing unit.

In a further, particularly advantageous embodiment, a lip for forming a recirculation zone is provided on the downstream end of the partition. This smaller recirculation zone is necessary to mix the richer and leaner areas in a small annular area directly in front of the mixing unit. In this recirculation zone, a ring of flame forms, which keeps the reaction in the burner going and prevents the flame from lifting.

In a particularly advantageous embodiment, the partition and the lip of the fuel nozzle system run tangentially through the inner region of the ignition device of the burner. An ignitable mixture is only formed immediately behind this lip, which is why the burner can only be ignited here directly after the gas has escaped.

The dividing wall and the lip of the fuel nozzle system can also run tangentially through the inner area of the flame monitoring device, since an ignitable mixture that can be ignited immediately is also present here.

A flame forms immediately behind the lip, which is necessary to monitor the flame with the help of an electrode. No flame signal can be measured by ionization at any other location than the one suggested.

In a further embodiment, the burner mouth leading into the combustion chamber is alternatively or cumulatively designed as a straight tube. Many known burners have a conical burner mouth. Although this has a positive effect on the flame stability, it causes strong turbulence and recirculation, which also has a negative effect on nitrogen oxide emissions.

It is also proposed that the substance, in particular the fuel from the channel system of the fuel nozzle system, meet the swirl of the oxidizer at a right angle. When the flows meet at a large angle, good oxidizer and fuel mixing is created. However, since fuel must in no way get downstream in front of the mixing unit, the maximum angle at which the two media may meet is 90 ° without the risk of fuel getting upstream in front of the mixing unit.

Finally, it is provided that the middle area of the mixing unit is designed in such a way that a UV sensor can detect the flame behind it.

Alternatively, the flame can also be monitored optically for monitoring with an electrode and an ionization signal. The prerequisite for this is that there is a peephole through which an optical sensor can detect the flame. In order to be able to visually monitor the flame despite the upstream perforated plate, a viewing tube is required from the end flange of the burner housing to the perforated plate.

Fig. 1

eine Gesamtansicht des zur Hälfte aufgeschnittenen Brenners mit doppelwandigem Rohr außerhalb des Gehäusequerschnitts

Fig. 2

eine Gesamtansicht des zur Hälfte ausgeschnittenen Brenners mit doppelwandigem Rohr innerhalb des Gehäusequerschnitts

Fig. 3

eine Gesamtansicht des Brennstoffdüsensystems mit doppelwandigem Rohr außerhalb des Gehäusequerschnitts von vorne

Fig. 4

einen Querschnitt des Brennstoffdüsensystems zur Definition des maximalen Drallwinkel (α) sowie zur Erläuterung der Bogenform des Drallelements und zur Erläuterung des nach innen abnehmenden Drallwinkels

Fig. 5

einen Querschnitt der Lippe zur Ausbildung einer Rezirkulationszone.

The invention is explained in more detail below with reference to the drawing. This shows in

Fig. 1

a general view of the burner cut open in half with a double-walled tube outside the cross-section of the housing

Fig. 2

a general view of the burner cut out in half with double-walled tube within the housing cross-section

Fig. 3

an overall view of the fuel nozzle system with a double-walled tube outside the housing cross-section from the front

Fig. 4

a cross section of the fuel nozzle system to define the maximum swirl angle (α) as well as to explain the arc shape of the swirl element and to explain the inwardly decreasing swirl angle

Fig. 5

a cross section of the lip to form a recirculation zone.

A burner, generally designated 1, has a housing 2 with a combustion tube 3, which has an opening 4 at the end remote from the housing 2. A fuel nozzle system 5 is arranged in the housing 2, the double-walled tube 15 of which lies outside the cross section of the housing 2. An ignition device 16 and a flame monitoring device 17 are located inside the housing 2, in which supports 19, 20 penetrate the fuel nozzle system 5 the flame monitoring 17 is penetrated.

Figure 2 shows a modified embodiment in which a fuel nozzle system 5 'is provided with a double-walled tube 15' arranged within the cross section of the housing 2.

Fig. 3 shows a plan view of the fuel nozzle system 5 with a double-walled tube 15 outside the cross section of the housing 2 from the front, that is to say from a downstream perspective. The outer ring 12, which is divided into 32 sub-segments, for example by larger fins 8, forms a first air cross-section 10 on the outside, while the inner ring 13, which is segmented, for example, by smaller fins 9 into 16 sub-areas, forms the air cross-section 11 on the inside. The inner circle also belongs to the inner air cross-section, cf. Fig. 3 .

Both area ratios of the inner ring 13, ie the air cross section 11 inside to the area ratio of the outer ring 12, ie the air cross section outside, is between 1: 2.5 to 1: 3.9, preferably exactly 1: 3.07. 1 area portion inside each to 3.1 area portions outside) Fig. 3 also shows an opening 14 for the carrier 19 of the ignition device 16 and a further opening 14 ′ for the carrier device of the flame monitoring device 17.

Fig. 4 shows a cross section of the fuel nozzle system 5 with an arcuate swirl element 21, in which the swirl angle (α) decreases from the outside to the inside, in the extreme case up to 0 °.

Fig. 5 finally shows a cut cross-section of the double-walled tube 15, 15 'with the two partial tubes 22, 23, a partition 24, the fuel channel 7 and 7' seen in the direction of flow of the oxidizer. At the downstream end 26 there is a lip 25 for forming a recirculation zone 27 in the downstream direction at the burner mouth 28.

Of course, the invention is not restricted to the exemplary embodiments shown. Further refinements are possible without departing from the basic idea.

List of reference symbols:

1

burner

2

casing

3

Burner tube

4th

opening

5, 5 '

Fuel nozzle system

6th

Oxidator channel

7, 7 '

Fuel channel

8th

larger slats

9

smaller slats

10

Air cross-section outside

11

Air cross-section inside

12

outer ring

13th

inner ring

14, 14 '

Breakthrough

15, 15 '

double-walled tube

16

Ignition device

17th

Flame control

18th

Perforated sheet

19th

carrier

20th

carrier

21st

curved swirl element

22nd

Partial pipe

23

Partial pipe

24

partition wall

25th

lip

26th

downstream end

27

Recirculation zone

28

Burner mouth

Claims (18)

Burner (1) with a housing (2) on which a combustion tube (3) is arranged, the combustion tube (3) having an opening (4) at the end facing away from the housing (2), and wherein the housing (2 ) has at least two separate channels (6, 7) through which different substances, in particular a fuel and an oxidizer, flow, which mix in a combustion chamber (8), the substances opening into a fuel nozzle system (5, 5 '), which is essentially circular and is set up in such a way that it produces a leaner mixture on at least one outer ring (12) and a richer mixture, in particular a fuel / oxidizer mixture, on at least one inner ring (13),
characterized,
that the elements of the fuel nozzle system (5, 5 ') are designed to be as thin, slim and streamlined as possible. Burner (1) according to claim 1,
characterized,
that the area ratio of the inner ring (13) to the area ratio of the outer ring (12) is 1: 2.5 to 1: 3.9, preferably 1: 3.1. Burner (1) according to claim 1, 2,
characterized,
that the maximum swirl angle (α) of the fuel nozzle system (5, 5 ') on the outside is between 30 ° to 60 °, preferably 48 °. Burner according to claim 1, 2 and / or 3,
characterized,
that the helix angle (α) decreases continuously from the outside to the inside. Burner (1) according to one or more of Claims 1-4
characterized,
that the swirl elements (21) are designed in an arc shape. Burner according to one or more of claims 1 - 5,
characterized,
that the helix angle (α) inside is "0". Burner according to one or more of claims 1-6,
characterized,
that the fuel nozzle system (5, 5 ') has a perforated plate (18) upstream for homogenizing the air flow upstream in front of the mixing unit over the entire cross section. Burner according to one or more of claims 1 - 7,
characterized,
that the installation space between the perforated plate (18) and the inner ring (13) has only electrodes, in particular an ignition device (16) and a flame monitor (17), and no other components. Burner according to one or more of claims 1 - 8,
characterized,
that at least one double-walled tube (15) for transporting fuel is arranged outside the housing cross-section (2) to the fuel nozzle system (5, 5 '). Burner according to one or more of claims 1 - 9,
characterized,
that at least one double-walled tube (15 ') is arranged on the very outside within the burner cross-section (2) for the transport of fuel on the edge of the housing cross-section (2) to the fuel nozzle system (5, 5'). Burner according to your or several claims 1 - 10,
characterized,
that the cross section of the swirl generator (21) is designed so that the fuel channel (7, 7 ') is led inwards. Burner according to one or more of claims 1-11,
characterized,
that a partition (24) is provided between the inner ring (13) and the outer ring (12) of the fuel nozzle system (5, 5 '). Burner according to claim 12,
characterized,
that a lip (25) for forming a recirculation zone (27) is provided at the downstream end (26) of the partition (24). Burner according to claim 12 and / or 13,
characterized,
that the partition (24) and the lip (25) of the fuel nozzle system (5, 5 ') run tangentially through the inner area of the ignition device (16) of the burner (1). Burner (1) according to at least one of claims 1-14,
characterized,
that the burner mouth (28) leading into the combustion chamber (8) is designed as a straight tube. Burner according to claims 12 - 15,
characterized,
that the partition (24) and the lip (25) of the fuel nozzle system (5, 5 ') run tangentially through the inner area of the flame monitoring device (17). Burner according to one or more of claims 1 - 16,
characterized,
that the substance, in particular the fuel, from the channel system of the fuel nozzle system (5, 5 ') hits the swirl of the oxidizer at a right angle. Burner according to one or more of claims 1-17,
characterized,
that the middle area of the fuel nozzle system (5, 5 ') is designed so that a UV sensor behind it can detect the flame.

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